It has been known to those in the concrete arts that the concrete goes through several chemical stages in its curing process before maximum concrete strength is attained.
Thus, during an initial set curing or hardening stage the Portland cement, appropriate inert fillers such as sand or gravel and water are mixed together with the proper proportions to give high strength concrete and proceed in a chemical reaction. This reaction is exothermic giving off internal heat. A 28 day hardening period is common in humid normal temperature ambient atmosphere, lasting until all the water and/or cement is chemically reacted. If there is not enough water some cement is wasted. If there is too much water the concrete strength is reduced. Thus, the amount of water is critical.
One common expedient in the art to aid the initial set curing process is to keep the concrete wet during the initial set stage. This serves two functions, keeping all the water in the mix to be used in the cement-water reaction, and to cool the concrete by evaporation.
It is also a known property of concrete that the chemical reactions in the curing process can be accelerated at higher temperatures. However, the higher temperatures also are critical and tend to cause cracking and deformation of shape during the initial set curing stage.
A residual store of hydrated lime results from this first stage chemical reaction, usually about 30% by weight of the cement. A following strength increasing carbonation stage thus takes place converting the lime, sometimes over several years. The CO.sub.2 of the air reacts to form calcium carbonates (CaCO.sub.3). In the ambient atmosphere the high strength of the concrete products is not reached quickly. Accordingly, it is known in the prior art to enrich the CO.sub.2 atmosphere about concrete articles to accelerate the carbonation stage.
It is an objective of the present invention to provide a manufacturing process for quickly (in a few hours) attaining high strength approaching maximum concrete products of critical shape such as block, tile and pipe.
There is no known satisfactory prior art process for quickly producing high strength concrete products by curing,drying and carbonation stages completed in a few hours.
Other significant and critical problems in the manufacture are also present in any attempt to shortcut the conventional process of atmospheric curing and carbonation, such as the cracking and/or shape distortion of the cement products and the energy efficiency of the manufacturing process.
Thus, other objectives, features and advantages of the invention will be found throughout the following description, drawing and claims.